This invention concerns polymers containing hyperbranched monomers, methods of preparing the polymers and use of the polymers for dewatering municipal and industrial sludges.
The dewatering of municipal and industrial sludges containing suspended organic solids is typically accomplished by mixing the sludge with one or more chemical reagents in order to induce a state of coagulation or flocculation of the solids which are then separated from the water using mechanical devices such as plate and frame filter presses, belt-filter presses, centrifuges, and the like.
For example, in a typical municipal sewage plant, waste water remaining after coarse solids are settled out of the incoming sewage influent is conveyed into a biological clarifying stage, where the dissolved and suspended organic material is decomposed by microorganisms in the presence or absence of air. These processes are referred to as aerobic fermentation and anaerobic fermentation, respectively.
The organic matter obtained as a result of this decomposition is largely bound in the form of a mass of microorganisms. This mass is precipitated as an activated sludge. The water may be released into waterways or allowed to seep away in sewage irrigation fields, but the activated sludge must be dewatered prior to disposal.
The objective of dewatering processes is to maximize the efficiency of water removal, as decreasing the amount of water retained in the dewatered solids leads decreased transport and disposal costs. Therefore, there is an ongoing need for improved dewatering technologies.
In its principal aspect, this invention is directed to a water-soluble, cationic polymer prepared by polymerizing from about 1 to about 65 mole percent of one or more cationic monomers, from about 99 to about 35 mole percent of one or more nonionic monomers and from about 1 to about 1000 ppm, based on the total monomer content, of one or more hyperbranched monomers.